System and Method for Open-Loop MIMO Communications in a SCMA Communications System

ABSTRACT

A method for transmitting data includes mapping a first coded information bit stream intended for a first transmit antenna onto at least one first spreading sequence of a plurality of first spreading sequences to generate a first data stream, mapping a second coded information bit stream intended for a second transmit antenna onto at least one second spreading sequence of a plurality of second spreading sequences to generate a second data stream. The method also includes transmitting the first data stream and the second data stream on respective transmit antennas.

This application is a continuation of U.S. patent application Ser. No.14/035,996, filed Sep. 25, 2013, entitled “System and Method forOpen-Loop MIMO Communications in a SCMA Communications System,” whichclaims the benefit of U.S. Provisional Application No. 61/737,338, filedon Dec. 14, 2012, entitled “Methods for Open-Loop MIMO Transmission andReception for SCMA OFDM Modulation,” all of which applications arehereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to digital communications, andmore particularly to a system and method for open-loop multiple input,multiple output (MIMO) communications in a sparse code multiple access(SCMA) communications system.

BACKGROUND

Code division multiple access (CDMA) is a multiple access technique inwhich data symbols are spread out over orthogonal and/or near orthogonalcode sequences. Traditional CDMA encoding is a two step process in whicha binary code is mapped to a quadrature amplitude modulation (QAM)symbol before a spreading sequence is applied. While traditional CDMAencoding can provide relatively high data rates, newtechniques/mechanisms for achieving even higher data rates are needed tomeet the ever-growing demands of next-generation wireless networks. Lowdensity spreading (LDS) is a form of CDMA used for multiplexingdifferent layers of data. LDS uses repetitions of the same symbol onlayer-specific nonzero position in time or frequency. As an example, inLDS-orthogonal frequency division multiplexing (OFDM) a constellationpoint is repeated (with some possible phase rotations) over nonzerofrequency tones of a LDS block. Sparse code multiple access (SCMA) is ageneralization of LDS where a multidimensional codebook is used tospread data over tones without necessarily repeating symbols.

SUMMARY OF THE DISCLOSURE

Example embodiments of the present disclosure which provide a system andmethod for open-loop MIMO communications in a SCMA communicationssystem.

In accordance with an example embodiment of the present disclosure, amethod for transmitting data is provided. The method mapping, by atransmitting device, a first coded information bit stream intended for afirst transmit antenna onto at least one first spreading sequence of aplurality of first spreading sequences to generate a first data stream,and mapping, by the transmitting device, a second coded information bitstream intended for a second transmit antenna onto at least one secondspreading sequence of a plurality of second spreading sequences togenerate a second data stream. The method also includes transmitting, bythe transmitting device, the first data stream and the second datastream on respective transmit antennas.

In accordance with another example embodiment of the present disclosure,a method for receiving data in a communications system is provided. Themethod includes determining, by a receiving device, a first plurality ofcodebooks and a second plurality of codebooks, wherein the firstplurality of codebooks and the second plurality of codebooks areassociated with a transmitting device transmitting user data to thereceiving device, and receiving, by the receiving device, a signalcarrying output codewords communicated over shared resources of thecommunications system, wherein each of the output codewords includes aplurality of codewords, wherein each of the plurality of codewordsbelongs to a different one of the plurality of codebooks, and whereineach of the plurality of codebooks is associated with a different one ofa plurality of data layers. The method also includes processing, by thereceiving device, the signal using the first plurality of codebooks andthe second plurality of codebooks in all of the plurality of data layersto recover the user data.

In accordance with another example embodiment of the present disclosure,a method for transmitting data is provided. The method includes mapping,by a transmitting device, a coded information bit stream intended for atransmit antenna onto at least one spreading sequence of a plurality ofspreading sequences to produce a data stream, and encoding, by thetransmitting device, the data stream using a space-time code to producea symbol block. The method also includes transmitting, by thetransmitting device, the symbol block.

In accordance with another example embodiment of the present disclosure,a method for receiving data is provided. The method includes receiving,by the receiving device, a symbol block from a transmitting devicetransmitting data to the receiving device, and processing, by thereceiving device, the symbol block using a space-time code and aplurality of codebooks associated with the transmitting device torecover the data.

In accordance with another example embodiment of the present disclosure,a transmitting device is provided. The transmitting device includes aprocessor, and a transmitter operatively coupled to the processor. Theprocessor maps a first coded information bit stream intended for a firsttransmit antenna onto at least one first spreading sequence of aplurality of first spreading sequences to generate a first data stream,and maps a second coded information bit stream intended for a secondtransmit antenna onto at least one second spreading sequence of aplurality of second spreading sequences to generate a second datastream. The transmitter transmits the first data stream and the seconddata stream on respective transmit antennas.

In accordance with another example embodiment of the present disclosure,a receiving device is provided. The receiving device includes aprocessor, and a receiver operatively coupled to the processor. Theprocessor determines a first plurality of codebooks and a secondplurality of codebooks, wherein the first plurality of codebooks and thesecond plurality of codebooks are associated with a transmitting devicetransmitting user data to the receiving device, and recovers a signalusing the first plurality of codebooks and the second plurality ofcodebooks in all of a plurality of data layers to recover the user data,the signal carrying output codewords communicated over shared resourcesof a communications system, wherein each of the output codewordsincludes a plurality of codewords, wherein each of the plurality ofcodewords belongs to a different one of the plurality of codebooks, andwherein each of the plurality of codebooks is associated with adifferent one of the plurality of data layers. The receiver receives thesignal.

One advantage of an embodiment is that increased spectral efficiency isachieved by combining SCMA with MIMO. Therefore, higher data rates maybe supported.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates an example communications system according to exampleembodiments described herein;

FIG. 2 illustrates an example communications system highlighting atransmitting device and receiving device according to exampleembodiments described herein;

FIG. 3 illustrates an example SCMA multiplexing scheme for encoding dataaccording to example embodiments described herein;

FIG. 4 a illustrates an example portion of a transmitting deviceaccording to example embodiments described herein;

FIG. 4 b illustrates an example flow diagram of high-level operationsoccurring in a transmitting device as the transmitting device transmitsusing open-loop MIMO code-space multiplexing for SCMA OFDM according toexample embodiments described herein;

FIG. 5 a illustrates an example flow diagram of operations occurring ina transmitting device as the transmitting device transmits to areceiving device using open-loop MIMO code-space multiplexing for SCMAOFDM according to example embodiments described herein;

FIG. 5 b illustrates an example flow diagram of operations occurring ina transmitting device as the transmitting device prepares multiplelayers of data to be transmitted using open-loop MIMO code-spacemultiplexing for SCMA OFDM according to example embodiments describedherein;

FIG. 5 c illustrates an example flow diagram of operations occurring ina transmitting device as the transmitting device prepares a layer ofdata to be transmitted using open-loop MIMO code-space multiplexing forSCMA OFDM according to example embodiments described herein;

FIG. 6 a illustrates an example flow diagram of operations occurring ina receiving device as the receiving device receives a transmission froma transmitting device where the transmission is transmitted usingopen-loop MIMO code-space multiplexing for SCMA OFDM according toexample embodiments described herein;

FIG. 6 b illustrates an example flow diagram of operations occurring ina receiving device with low receiver complexity as the receiving devicereceives a transmission from a transmitting device where thetransmission is transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM according to example embodiments described herein;

FIG. 6 c illustrates an example flow diagram of operations occurring ina receiving device with medium receiver complexity as the receivingdevice receives a transmission from a transmitting device where thetransmission is transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM according to example embodiments described herein;

FIG. 6 d illustrates an example flow diagram of operations occurring ina receiving device with high receiver complexity as the receiving devicereceives a transmission from a transmitting device where thetransmission is transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM according to example embodiments described herein;

FIG. 7 a illustrates an example portion of a communications system witha receiving device with low receiver complexity according to exampleembodiments described herein;

FIG. 7 b illustrates an example portion of a communications system witha receiving device with medium receiver complexity according to exampleembodiments described herein;

FIG. 8 illustrates an example portion of a communications system with areceiving device with high receiver complexity according to exampleembodiments described herein;

FIG. 9 illustrates an example portion of a communications system whereinterference management is performed using signature and/or codebook setassignment according to example embodiments described herein;

FIG. 10 a illustrates an example communications system whereinter-transmitter coordinated beamforming (CBF) is used with open-loopMIMO CSM according to example embodiments described herein;

FIG. 10 b illustrates an example communications system whereintra-transmitter coordinated beamforming (CBF) is used with open-loopMIMO CSM according to example embodiments described herein;

FIG. 11 a illustrates an example model of a transmittingdevice-receiving device pair used in block-wise space-time coding inMIMO SCMA where the receiving device has low complexity according toexample embodiments described herein;

FIG. 11 b illustrates an example model of a transmittingdevice-receiving device pair used in block-wise space-time coding inMIMO SCMA where the receiving device has high complexity according toexample embodiments described herein

FIG. 12 a illustrates an example flow diagram of operations occurring ina transmitting device as the transmitting device transmits data usingblock-wise space-time coding according to example embodiments describedherein;

FIG. 12 b illustrates an example flow diagram of operations occurring ina receiving device with low complexity as the receiving device receivesdata using block-wise space-time coding according to example embodimentsdescribed herein;

FIG. 12 c illustrates an example flow diagram of operations occurring ina receiving device with high complexity as the receiving device receivesdata using block-wise space-time coding according to example embodimentsdescribed herein;

FIG. 13 a illustrates an example symbol of an example MIMO SCMA OFDMcommunications system according to example embodiments described herein;

FIG. 13 b illustrates an example model of a transmittingdevice-receiving device pair using an Alamouti algorithm for block-wisespace-time coding according to example embodiments described herein;

FIG. 14 illustrates an example first communications device according toexample embodiments described herein;

FIG. 15 illustrates an example second communications device according toexample embodiments described herein;

FIG. 16 illustrates an example third communications device according toexample embodiments described herein; and

FIG. 17 illustrates an example fourth communications device according toexample embodiments described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The operating of the current example embodiments and the structurethereof are discussed in detail below. It should be appreciated,however, that the present disclosure provides many applicable inventiveconcepts that can be embodied in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificstructures of the disclosure and ways to operate the disclosure, and donot limit the scope of the disclosure.

One embodiment of the disclosure relates to open-loop MIMOcommunications in a SCMA communications system. For example, atransmitting device maps a first coded information bit stream intendedfor a first transmit antenna onto at least one first spreading sequenceof a plurality of first spreading sequences to generate a first datastream, maps a second coded information bit stream intended for a secondtransmit antenna onto at least one second spreading sequence of aplurality of second spreading sequences to generate a second datastream, and transmits the first data stream and the second data streamon respective transmit antennas. As another example, a receiving devicedetermines a first plurality of codebooks and a second plurality ofcodebooks, wherein the first plurality of codebooks and the secondplurality of codebooks are associated with a transmitting devicetransmitting user data to the receiving device, receives a signalcarrying output codewords communicated over shared resources of thecommunications system, wherein each of the output codewords includes aplurality of codewords, wherein each of the plurality of codewordsbelongs to a different one of the plurality of codebooks, and whereineach of the plurality of codebooks is associated with a different one ofa plurality of data layers, and processes the signal using the firstplurality of codebooks and the second plurality of codebooks in all ofthe plurality of data layers to recover the user data.

The present disclosure will be described with respect to exampleembodiments in a specific context, namely a SCMA communications systemthat supports MIMO to increase spectral efficiency. The disclosure mayalso be applied, however, to standards compliant and non-standardscompliant SCMA communications systems that support MIMO to increasespectral efficiency.

SCMA is an encoding technique that encodes data streams, such as binarydata streams, or in general, M-ary data streams, where M is an integernumber greater than or equal to 2) into multidimensional codewords. SCMAdirectly encodes the data stream into multidimensional codewords andcircumvents quadrature amplitude modulation (QAM) symbol mapping, whichmay lead to coding gain over conventional CDMA encoding. Notably, SCMAencoding techniques convey data streams using a multidimensionalcodeword rather than a QAM symbol.

Additionally, SCMA encoding provides multiple access through the use ofdifferent codebooks for different multiplexed layers, as opposed to theuse of different spreading sequences for difference multiplexed layers,e.g., a LDS signatures in LDS, as is common in conventional CDMAencoding. Furthermore, SCMA encoding typically uses codebooks withsparse codewords that enable receivers to use low complexity algorithms,such as message passing algorithms (MPA), to detect respective codewordsfrom combined codewords received by the receiver, thereby reducingprocessing complexity in the receivers.

FIG. 1 illustrates a communications system 100. Communications system100 may support SCMA communications. Communications system 100 includesan enhanced NodeB (eNB) 105, as well as eNB 107, serving a plurality ofuser equipments (UE). eNB 105 may be an example of a communicationscontroller, which may also be referred to as a controller, a basestation, a NodeB, and the like. UEs may be examples of communicatingdevices, which may also be referred to as mobile stations, terminals,users, subscribers, and the like. eNBs 105 and 107 may include multipletransmit antennas and multiple receive antennas to facilitate MIMOoperation, wherein a single eNB may simultaneously transmit multipledata streams to multiple users, a single user also with multiple receiveantennas, or a combination thereof. Similarly, the UEs may includemultiple transmit antennas and multiple receive antennas to support MIMOoperation. It is noted that although shown in FIG. 1 as being a singleentity with multiple transmit antennas, eNBs with multiple transmitantennas may have their transmit antennas located at a single device ordistributed across multiple devices. In a distributed situation, an eNBmay control the operation of the distributed devices. The same may betrue for UEs with multiple transmit antennas. When a single device iscapable of simultaneously transmitting to multiple users, the singledevice may be referred to as operating in a multiple user MIMO (MU-MIMO)mode.

While it is understood that communications systems may employ multipleeNBs capable of communicating with a number of UEs, only two eNBs, and anumber of UEs are illustrated for simplicity.

FIG. 2 illustrates a communications system 200 highlighting atransmitting device 205 and receiving device 210. In general, atransmitting device may refer to an eNB making a downlink transmissionto a UE or a UE making an uplink transmission to an eNB, and a receivingdevice may refer to a UE receiving a downlink transmission from an eNBor an eNB receiving an uplink transmission from a UE. Transmittingdevice 205 has J transmit antennas (shown as TX₁ through TX_(J)) whilereceiving device 210 has K receive antennas (shown as RX₁ throughRX_(K)), where J and K are integer numbers greater than or equal to 1(however, for MIMO transmission, J and K are generally greater than orequal to 2). As shown in FIG. 2, transmitting device 205 has as input Mdata streams, where M is an integer number greater than or equal to 1,that are transmitted over the K transmit antenna to receiving device210. Receiving device 210 decodes the received signal to reconstruct theM data streams. It is noted that the transmission of M data streams to asingle receiving device is intended for illustrative purposes only,since with J transmit antenna, transmitting device 205 may transmit toup to M receiving devices.

FIG. 3 illustrates an example SCMA multiplexing scheme 300 for encodingdata. As shown in FIG. 3, SCMA multiplexing scheme 300 may utilize aplurality of codebooks, such as codebook 310, codebook 320, codebook330, codebook 340, codebook 350, and codebook 360. Each codebook of theplurality of codebooks is assigned to a different multiplexed layer.Each codebook includes a plurality of multidimensional codewords (orspreading sequences). It is noted that in LDS, the multidimensionalcodewords are low density sequence signatures. More specifically,codebook 310 includes codewords 311-314, codebook 320 includes codewords321-324, codebook 330 includes codewords 331-334, codebook 340 includescodewords 341-344, codebook 350 includes codewords 351-354, and codebook360 includes codewords 361-364.

Each codeword of a respective codebook may be mapped to a differentdata, e.g., binary, value. As an illustrative example, codewords 311,321, 331, 341, 351, and 361 are mapped to binary value ‘00’, thecodewords 312, 322, 332, 342, 352, and 362 are mapped to the binaryvalue ‘01’, the codewords 313, 323, 333, 343, 353, and 363 are mapped tothe binary value ‘10’, and the codewords 314, 324, 334, 344, 354, and364 are mapped to the binary value ‘11’. It is noted that although thecodebooks in FIG. 3 are depicted as having four codewords each, SCMAcodebooks in general may have any number of codewords. As an example,SCMA codebooks may have 8 codewords (e.g., mapped to binary values ‘000’. . . ‘111’), 16 codewords (e.g., mapped to binary values ‘0000’ . . .‘1111’), or more.

As shown in FIG. 3, different codewords are selected from variouscodebooks 310, 320, 330, 340, 350, and 360 depending on the binary databeing transmitted over the multiplexed layer. In this example, codeword314 is selected from codebook 310 because the binary value ‘11’ is beingtransmitted over the first multiplexed layer, codeword 322 is selectedfrom codebook 320 because the binary value ‘01’ is being transmittedover the second multiplexed layer, codeword 333 is selected fromcodebook 330 because the binary value ‘10’ is being transmitted over thethird multiplexed layer, codeword 342 is selected from codebook 340because the binary value ‘01’ is being transmitted over the fourthmultiplexed layer, codeword 352 is selected from codebook 350 becausethe binary value ‘01’ is being transmitted over the fifth multiplexedlayer, and codeword 364 is selected from codebook 360 because the binaryvalue ‘11’ is being transmitted over the sixth multiplexed layer.Codewords 314, 322, 333, 342, 352, and 364 may then be multiplexedtogether to form multiplexed data stream 380, which is transmitted overshared resources of a network. Notably, codewords 314, 322, 333, 342,352, and 364 are sparse codewords, and therefore can be identified uponreception of multiplexed data stream 380 using a low complexityalgorithm, such as a message passing algorithm (MPA) or a turbo decoder.

According to an example embodiment, it is possible to combine SCMAmodulation with MIMO to improve spectral efficiency. A variety of MIMOtransmission and reception techniques for SCMA orthogonal frequencydivision multiplex (OFDM) modulation are provided, including: MIMO forcode-space multiplexing (CSM) with open-loop single user (SU) andmulti-user (MU) MIMO techniques with spreading in multi-carrier timeand/or frequency domain; open-loop MIMO techniques for inter-transmitpoint (TP) and intra-TP interference coordination including CSM withsignature and/or codebook coordination and/or coordinated beam forming(CBF)/CSM; and MIMO for transmit diversity including block-wisespace-time coding (e.g., Alamouti technique) combined with SCMA toachieved double domain diversity (space and time and/or frequencydomains). The combination of SCMA modulation with MIMO providesadvantages over conventional techniques, such as code-domainmultiplexing (e.g., code division multiple access, low densitysignatures, SCMA, and the like), multicarrier modulation (e.g., OFDM),open-loop MIMO schemes, coordinated multi-point (CoMP), and the like.

FIG. 4 a illustrates a portion of a transmitting device 400.Transmitting device 400 supports open-loop MIMO code-space multiplexingfor SCMA OFDM. As shown in FIG. 4, spreading occurs over the time and/orfrequency domain. Transmitting device 400 supports the transmission ofdata to up to N*J users, denoted U₁ . . . U_(NJ), where N and J are aninteger number greater than or equal to 1. It is noted that a singledevice may comprise one or more users; therefore, transmitting device400 may support transmissions to up to N*J unique devices. Transmissiondevice 400 also includes N transmit antenna, denoted TX₁ 405 . . .TX_(N) 407.

Data for a single user is mapped (or encoded) using a signature and/orcodebook set. As an example, data transmitted from antenna 1 (denoted U₁410) includes up to J data layers, denoted U₁₁ . . . U_(1J), is mapped(or encoded) using a signature and/or codebook set S₁ 415. Signatureand/or codebook set S₁ 415 includes J sub-signatures and/orsub-codebooks, denoted S₁₁ . . . S_(1J), with a sub-signature and/orsub-codebook assigned to one of the J data layers, where J is an integernumber greater than or equal to 1. As shown in FIG. 4 a, sub-signatureand/or sub-codebook S₁₁ is assigned to data layer U₁₁, sub-signatureand/or sub-codebook S_(1J) is assigned to data layer U_(1J). As anotherexample, data transmitted from antenna N (denoted U_(N) 412) includes upto J data layers, denoted U_(N1) . . . U_(NJ), is mapped (or encoded)using a signature and/or codebook set S_(N) 417. Signature and/orcodebook set S_(N) 417 includes J sub-signatures and/or sub-codebooks,denoted S_(N1) . . . S_(NJ). As an illustrative example, a value of anumber of bits of data layer U₁₁ may be used to index into sub-signatureand/or sub-codebook S₁₁ (which is associated with data layer U₁₁) and acodeword corresponding to the value of the number of bits of data layerU₁₁ is a mapped (or encoded) representation of the value of the numberof bits of data layer U₁₁. It is noted that the data as well assignature and/or codebook sets may be completely disjoint, completelythe same, or have partial overlap. Overlap between the data determines atradeoff between diversity and spectral efficiency resulting frommultiplexing, while overlap in between the signature and/or codebooksets determines codebook utilization (or codebook utilization factor) inthe communications system.

The mapped (or encoded) data may be combined prior to transmission by arespective transmit antenna. The mapped (or encoded) data may be in theform of a bit stream or a data stream. As an example, the mapped (orencoded) data to be transmitted from antenna 1 may be combined bycombiner 420, which may combine the mapped (or encoded) data together toproduce multiplexed codewords that are transmitted by transmit antennaTX₁ 405. As another example, if the data comprises only a single layer,a mapper may be used to map the mapped (or encoded) data onto outputcodewords that are subsequently transmitted. A combiner 422 combines,e.g., combines or maps, the corresponding mapped (or encoded) data priorto transmission by transmit antenna TX_(N) 407.

FIG. 4 b illustrates a flow diagram of high-level operations 450occurring in a transmitting device as the transmitting device transmitsusing open-loop MIMO code-space multiplexing for SCMA OFDM. Operations450 may be indicative of operations occurring in a transmitting device,such as transmitting device 205, as the transmitting device transmitsusing open-loop MIMO code-space multiplexing.

Operations 450 may begin with the transmitting device determining acodebook set S_(Q) for a transmit antenna Q of the transmitting device(block 455). The codebook set S_(Q) may include J sub-codebooks (denotedS_(Q1) . . . S_(QJ)) with a sub-codebook for each data layer transmittedby the transmit antenna, where Q and J are integer values and J is thenumber of data layers transmitted per transmit antenna. Typically, thecodebook set S_(Q) may be specified by a technical standard, selected byan operator of a communications system including the transmittingdevice, or a combination thereof. As an example, the technical standardmay specify a plurality of codebook sets and the operator of thecommunications system may select a codebook set for the transmitantennas of the transmitting device out of the plurality of codebooksets. Each transmit antenna may be assigned a different codebook set,all of the transmit antennas may be assigned a single codebook set, orsome transmit antennas may be assigned a single codebook set whileothers may be assigned different codebook sets. The codebook set and/orthe plurality of codebook sets may be stored in a memory or a server andmay be provided to the transmitting device or retrieved by thetransmitting device at association and/or periodically signaled orindicated to the transmitting device. The transmitting device mayperform a check to determine if there are more transmit antennas withoutcodebook sets (block 460). If there is one or more transmit antennaswithout codebook sets, the transmitting device may return to block 465to assign a codebook set to another transmit antenna.

The transmitting device may map (or encode) data for each of thetransmit antennas a code space multiplexing (CSM) technique (block 465).CSM may involve the use of the codebook set(s) assigned to the transmitantennas to map (or encode) the data to be transmitted on each of thetransmit antennas. Generally, data for each transmit antenna may be inthe form of a bit stream and may include data for each of J data layers.The data for the transmit antenna may be partitioned into the Jrespective data layers and then the data for the each of the J datalayers may be subpartitioned into transmission unit sized parts. As anillustrative example, if the transmission units are two-bits in size,the data for each of the J data layers may be subpartitioned intotwo-bit parts. A value of each of the transmission unit sized parts maybe used to select a codeword (e.g., a spreading sequence) in asub-codebook associated with the transmit antenna. The sub-codebookcomprises a plurality of codewords (e.g., spreading sequences). Thesub-codebooks are part of a set of codebooks. The selection of thecodeword in the sub-codebook using the value of each of the transmissionunit sized parts may be referred to as mapping (or encoding). As anexample, if the value of a particular two-bit transmission unit sizepart for a data layer is “00”, a codeword in the sub-cookbook associatedwith the data layer that corresponds to value “00” is selected as mapped(or encoded) data for the particular two-bit transmission unit size. Itis noted that in a single data layer case (i.e., J=1), there is a singlesub-codebook in the set of codebooks.

The transmitting device may combine the encoded data for the variousdata layers of a transmit antenna to produce output codewords (block470). As discussed previously, the transmitting device may combine theencoded data by multiplexing the encoded data together, producing theoutput codewords, which may be in the form of a bit stream or a datastream. The transmitting device may transmit the output codewords on therespective transmit antennas (block 475). As an example, the transmitdevice may transmit an output codeword associated with a particulartransmit antenna using the transmit antenna, such as output codeword Qfor transmit antenna Q.

FIG. 5 a illustrates a flow diagram of operations 500 occurring in atransmitting device as the transmitting device transmits to a receivingdevice using open-loop MIMO code-space multiplexing for SCMA OFDM.Operations 500 may be indicative of operations occurring in atransmitting device, e.g., an eNB making a downlink transmission or a UEmaking an uplink transmission, as it transmits to a receiving device.

Operations 500 may begin with the transmitting device determining dataor data layers to be transmitted by transmit antenna i, denoted U_(i)(block 505). The determination of the data or data layers to betransmitted by transmit antenna i may be made in accordance with inputdata that is to be transmitted, as well as performance requirements forthe input data, such as quality of service (QoS) requirements, receivingdevice priority, network condition, priority of other receiving devicesserved by the transmitting device, input data availability, and thelike. The transmitting device may also determine a signature and/orcodebook set to be used for spread the data or data layers for eachtransmit antenna i (block 507). The signature and/or codebook set,denoted S_(i), may be determined in accordance with a codebookutilization factor. As an example, if the codebook utilization factor isto be high, then an overlap in the signature and/or codebook set S_(i)and other signature and/or codebook sets used in the communicationsystem is significant. While, if the codebook utilization factor is tobe low, then the overlap in the signature and/or codebook set S_(i) andother signature and/or codebook sets used in the communication system isinsignificant or zero.

The transmitting device may encode the data or data layers to betransmitted by each transmit antenna with its associated signatureand/or codebook set and combine the encoded data for each transmitantenna to form a signal to be transmitted by the transmit antenna(block 509). As discussed previously, each data layer to be transmittedby a transmit antenna may be encoded using a sub-signature and/orsub-codebook from the signature and/or codebook set associated with thetransmit antenna. The encoded data may be combined, e.g., multiplexed ormapped, to form output codewords that are transmitted by the transmitantenna. As an example, the data layers of the input data to betransmitted by transmit antenna i may be encoded using signature and/orcodebook S_(i) and then combined by a combiner associated with transmitantenna i prior to being transmitted by transmit antenna i.

FIG. 5 b illustrates a flow diagram of operations 520 occurring in atransmitting device as the transmitting device prepares multiple layersof data to be transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM. Operations 520 may be indicative of operations occurringin a transmitting device, e.g., an eNB making a downlink transmission ora UE making an uplink transmission, as it prepares data to betransmitted to a receiving device. Operations 520 may be an exampleembodiment of block 509 of FIG. 5 a.

Operations 520 may begin with the transmitting device receiving data foreach transmit antenna (block 525). In general, the data for transmitantenna i is denoted U_(i) and may include multiple data layers. Thetransmitting device may select one of its N transmit antennas (block527) and map (or encode) data for the respective data layers using asignature and/or codebook set associated with the selected transmitantenna, producing encoded codewords (block 529). As an example, datafor a data layer may have a value and the value may be used to indexinto a sub-signature and/or sub-codebook for the data layer to select asignature and/or codeword associated with the value. The selectedsignature and/or codeword may be used as an encoded codeword for thedata layer. The transmitting device may combine (e.g., multiplex) theencoded codewords to produce an output codeword (block 531).

The transmitting device may perform a check to determine if there moretransmit antennas that have not had their data encoded (block 533). Ifthere are more transmit antennas, the transmitting device may return toblock 527 to select another transmit antenna. If there are no moretransmit antennas, the transmitting device may transmit the outputcodewords on respective transmit antennas (block 535).

FIG. 5 c illustrates a flow diagram of operations 540 occurring in atransmitting device as the transmitting device prepares a layer of datato be transmitted using open-loop MIMO code-space multiplexing for SCMAOFDM. Operations 540 may be indicative of operations occurring in atransmitting device, e.g., an eNB making a downlink transmission or a UEmaking an uplink transmission, as it prepares data to be transmitted toa receiving device. Operations 540 may be an example embodiment of block509 of FIG. 5 a.

Operations 540 may begin with the transmitting device receiving data foreach transmit antenna (block 545). In general, the data for transmitantenna i is denoted U_(i) and may include a single data layer. Thetransmitting device may select one of its N transmit antennas (block547) and map (or encode) data for the data layer using a signatureand/or codebook set associated with the selected transmit antenna,producing encoded codewords (block 549). As an example, data for thedata layer may have a value and the value may be used to index into asub-signature and/or sub-codebook for the data layer to select asignature and/or codeword associated with the value. The selectedsignature and/or codeword may be used as an encoded codeword for thedata layer. The transmitting device may map the encoded codeword using amapping rule associated with the transmit antenna to produce an outputcodeword (block 551).

The transmitting device may perform a check to determine if there moretransmit antennas that have not had their data encoded (block 553). Ifthere are more transmit antennas, the transmitting device may return toblock 547 to select another transmit antenna. If there are no moretransmit antennas, the transmitting device may transmit the outputcodewords on respective transmit antennas (block 555).

FIG. 6 a illustrates a flow diagram of operations 600 occurring in areceiving device as the receiving device receives a transmission from atransmitting device where the transmission is transmitted usingopen-loop MIMO code-space multiplexing for SCMA OFDM. Operations 600 maybe indicative of operations occurring in a receiving device, e.g., a UEreceiving a downlink transmission from an eNB or an eNB receiving anuplink transmission from a UE, as the receiving device receives atransmission from a transmitting device. Operations 600 may provide ahigh-level view of receiving a transmission when the transmission ismade using open-loop MIMO code-space multiplexing for SCMA OFDM.

Operations 600 may begin with the receiving device determining one ormore plurality of codebooks (block 602). As an example, the receivingdevice may determine the one or more plurality of codebooks inaccordance with identifying information of a transmitting device(s) thatis transmitting to the receiving device. The identifying information mayinclude an identifier (ID) or identifiers (IDs) of the transmittingdevice(s), cell ID, cell IDs, and the like. The receiving device may usethe identifying information to determine the one or more plurality ofcodebooks. As an illustrative example, the receiving device may haveobtained codebook assignments from its serving eNB during an initialassociation or retrieved the codebook assignments during power up. Thereceiving device may utilize the codebook assignment and the identifyinginformation to determine the one or more plurality of codebooks used toencode the transmissions from the transmitting device(s).

The receiving device may receive a signal transmitted by thetransmitting device (block 605). The signal may include output codewordsand may be communicated over shared resources of the communicationssystem. The receiving device may process the received signal in allspatial layers to recover data transmitted in the signal (block 607). Ingeneral, the receiving device may feature multiple receive antenna totake full advantage of open-loop MIMO code-space multiplexing for SCMAOFDM. Hence, the processing performed by the receiving device to recoverthe transmitted data may be more complex than processing typicallyinvolved in recovering transmitted data when the receiving device has asingle antenna or when multiple spatial layers are not used.

According to an example embodiment, the processing performed by thereceiving device may differ depending on the complexity and/orcapability of the receiving device. As an example, a low complexityand/or low capability processing technique may be utilized in arelatively inexpensive UE, while a high complexity and/or highcapability processing technique may be used in a high-end UE or an eNB.Furthermore, a compromise midline complexity and/or midline capabilityprocessing technique may be used. In general, the use of a highcomplexity and/or high capability processing technique may result inbetter performance, while a low complexity and/or low capabilityprocessing technique may yield lower performance. Therefore, a trade-offmay be made between performance and complexity.

FIG. 6 b illustrates a flow diagram of operations 620 occurring in areceiving device with low receiver complexity as the receiving devicereceives a transmission from a transmitting device where thetransmission is transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM. Operations 620 may be indicative of operations occurringin a receiving device, e.g., a UE receiving a downlink transmission froman eNB or an eNB receiving an uplink transmission from a UE, as thereceiving device receives a transmission from a transmitting device.Operations 620 may be a detailed implementation of operations 600 ofFIG. 6 a.

Operations 620 may begin with the receiving device receiving a signaltransmitted by the transmitting device (block 625). The receiving devicemay determine a baseband signal of the received signal over the receiveantennas of the receiving device and the bandwidth for the receivedsignal (block 627). The baseband signal may be a version of the receivedsignal that has been down converted from a carrier frequency. With lowreceiver complexity, the receiving device may not be capable ofperforming complicated processing on the baseband signal whilemaintaining desired performance. Therefore, the processing of thebaseband signal may take place in distinct stages.

The receiving device may separate the different data layers of thebaseband signal in the spatial domain (block 629). In other words, thereceiving device may separate the baseband signal into a plurality ofdifferent sub-signals, with one sub-signal per spatial layer. Thereceiving device may use a MIMO receiver, e.g., a minimum mean squareerror (MMSE) receiver, to separate the different data layers of thebaseband signal in the spatial domain. The receiving device may decodedata in the baseband signal on a per spatial layer basis (block 631).The receiving device may use a SCMA detector to separately decode dataon each spatial layer. It is noted that each spatial layer may bedecoded using a separate SCMA detector. As an example, the SCMA detectormay implement a MPA along with turbo decoding algorithm. FIG. 7 aillustrates a portion of a communications system 700 with a receivingdevice 705 with low receiver complexity. Transmitting antennas 710 of atransmitting device transmits data, which are received by receivingantennas 715 of receiving device 705. A baseband signal of the receivedsignal may be provided to a MIMO receiver 720 which separates themultiple data layers into M spatial layers, where M is an integer numbergreater than or equal to 1. Each of the M spatial layers may be providedto one of M SCMA detectors, such as SCMA detector 725. The M SCMAdetectors decode their respective spatial layer to produce M datastreams, which may be further processed by receiving device 705.

FIG. 6 c illustrates a flow diagram of operations 640 occurring in areceiving device with medium receiver complexity as the receiving devicereceives a transmission from a transmitting device where thetransmission is transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM. Operations 640 may be indicative of operations occurringin a receiving device, e.g., a UE receiving a downlink transmission froman eNB or an eNB receiving an uplink transmission from a UE, as thereceiving device receives a transmission from a transmitting device.Operations 640 may be a detailed implementation of operations 600 ofFIG. 6 a.

Operations 640 may begin with the receiving device receiving a signaltransmitted by the transmitting device (block 645). The receiving devicemay determine a baseband signal of the received signal over the receiveantennas of the receiving device and the bandwidth for the receivedsignal (block 647). The receiving device may separate the different datalayers in the baseband signal as well as partially cancel interferencebetween spatial layers (block 649). The receiving device may use a MIMOreceiver to perform the partial separation of the data layers and thepartial cancellation of interference. As an illustrative example, a MIMOreceiver may be selected so that noise enhancement due to the MIMOreceiver is minimized. The receiving device may decode data in thebaseband signal on a per spatial layer basis (block 651). The receivingdevice may exchange log likelihood ratios (LLRs) between decoders untilthe data is decoded. The receiving device may use a SCMA detector, e.g.,a MPA detector, to separately decode data on each spatial layer. It isnoted that as few as two SCMA detectors may be needed. Any remaininginterference not removed by the MIMO receiver may be removed bycooperation between the SCMA detectors, such as MPA decoders.

According to an example embodiment where a receiving device has mediumreceiver complexity, the receiving device may implement MIMO receiver toperform QR decomposition on the spatial layers. As an example, in thecase of a two by two MIMO system with two spatial layers, the basebandsignal in the received signal may be expressed as: y=H x+n in which Hrepresents the channel matrix, x is the transmitted SCMA signals and nis the noise. Using QR decomposition, H may be written as Q*R in which Qis a unitary matrix and R is an upper triangular matrix which may beexpressed as

$\begin{bmatrix}R_{11} & R_{12} \\0 & R_{22}\end{bmatrix}.$

The MIMO receiver may be represented as the transpose conjugate of Q.After the MIMO receiver, the second spatial layer does not see anyinterference from the first spatial layer and may be decoded using aSCMA detector, e.g., a MPA detector. After decoding, the LLRscorresponding to the second spatial layer may be considered whiledecoding the first spatial layer using a SCMA detector, e.g., a MPAdetector. The procedure may be performed iteratively until all of datahas been decoded.

FIG. 7 b illustrates a portion of a communications system 750 with areceiving device 755 with medium receiver complexity. Transmittingantennas 760 of a transmitting device transmits data, which are receivedby receiving antennas 765 of receiving device 755. A baseband signal ofthe received signal may be provided to a MIMO receiver 770 whichseparates the multiple data layers into M spatial layers, where M is aninteger number greater than or equal to 1. Each of the M spatial layersmay be provided to one of M SCMA detectors, such as SCMA detector 775.The M SCMA detectors decode their respective spatial layer to produce Mdata streams, which may be further processed by receiving device 755.The M SCMA detectors may exchange LLRs until the data is decoded.

FIG. 6 d illustrates a flow diagram of operations 660 occurring in areceiving device with high receiver complexity as the receiving devicereceives a transmission from a transmitting device where thetransmission is transmitted using open-loop MIMO code-space multiplexingfor SCMA OFDM. Operations 660 may be indicative of operations occurringin a receiving device, e.g., a UE receiving a downlink transmission froman eNB or an eNB receiving an uplink transmission from a UE, as thereceiving device receives a transmission from a transmitting device.Operations 660 may be a detailed implementation of operations 600 ofFIG. 6 a.

Operations 660 may begin with the receiving device receiving a signaltransmitted by the transmitting device (block 665). The receiving devicemay determine a baseband signal of the received signal over the receiveantennas of the receiving device and the bandwidth for the receivedsignal (block 667). The receiving device may decode data on all spatiallayers of the baseband signal (block 669). The receiving device may usea joint MIMO receiver, e.g., a maximal ratio combiner (MRC), and a SCMAdecoder, e.g., a MPA decoder, for all spatial layers. The receivingdevice may have the same structure as a single spatial layer SCMAdecoder where the number of SCMA layers is multiplied by the number ofspatial layers. In situations where interference between the layersdegrades performance, additional outer loop iterations and/or poweroffsets between spatial layers or transmit antennas may help improveperformance. FIG. 8 illustrates a portion of a communications system 800with a receiving device 805 with high receiver complexity. Transmittingantennas 810 of a transmitting device transmits data, which are receivedby receiving antennas 815 of receiving device 805. A baseband signal ofthe received signal may be provided to a joint MIMO receiver and SCMAdetector 820 which decodes the baseband signal with all of its spatiallayers to produce M data streams, which may be further processed byreceiving device 805. As an example, joint MIMO receiver and SCMAdetector 820 may implement a MRC receiver and a MPA decoder.

FIG. 9 illustrates a portion of a communications system 900 whereinterference management is performed using signature and/or codebook setassignment. As shown in FIG. 9, three transmitting devices, transmitter905, transmitter 907, and transmitter 909, are shown actively makingtransmissions. In general, transmissions from transmitting devices thatare relatively close to a receiving device, such as UE 915, may causeinterference to the receiving device. A variety of techniques such asfractional frequency reuse, beam shaping, beamforming, and the like,have been proposed to help reduce or eliminate interference. Fordiscussion purposes, consider a situation as shown in FIG. 9, wherefirst transmissions from multiple transmit antennas of transmitter 905arrive at UE 915 as signals 920, second transmissions from multipletransmit antennas of transmitter 907 arrive at UE 915 as signals (ifjoint transmission (JT) is used) or decodable interference 925, andthird transmissions from multiple transmit antennas of transmitter 909arrive at UE 915 as interference 930.

According to an example embodiment, it may be possible to performmulti-transmission point interference management through signatureand/or codebook set assignment. As an example, it may be possible toassign different signature and/or codebook sets to different transmitantennas at each transmitting device. With such a configuration, eachtransmit antenna uses a different signature and/or codebook set tomultiplex SCMA signals. It is noted that for uncorrelated antennas, itis possible to share the same signature and/or codebook set.Furthermore, different transmitting devices may use the same signatureand/or codebook sets or different signature and/or codebook sets. Insuch a configuration, the receiving device may jointly detect signalsfrom multiple transmitting devices and if a signal from a transmittingdevice is sufficiently weak, it may be automatically treated asinterference. Additionally, transmitting devices may jointly transmitthe same data over some CSM layers to improve diversity for receivingdevices operating with poor signal conditions. Such transmitting devicesmay use joint transmission (JT) processing techniques with the samesignature and/or codebook sets.

For discussion purposes, consider a situation as shown in FIG. 9, wherefirst transmissions from multiple transmit antennas of transmitter 905arrive at UE 915 as signals 920, second transmissions from multipletransmit antennas of transmitter 907 arrive at UE 915 as signals (ifjoint transmission (JT) is used) or decodable interference 925, andthird transmissions from multiple transmit antennas of transmitter 909arrive at UE 915 as interference 930. Transmitter 905 and transmitter907 are using JT processing to transmit the same data to UE 915 with thesame signature and/or codebook sets. Therefore, UE 915 may be able touse diversity to improve its relatively poor signal condition.Transmitter 909 is relatively far away from UE 915, so its signalsarrive at UE 915 having low signal strength and UE 915 may considertransmissions from transmitter 909 as interference 930. Similarly, iftransmissions from transmitter 907 arrive at UE 915 with low signalstrength, UE 915 may consider those transmissions as interference.

The communications system, an entity in the communications system, anoperator of the communications system, a technical standard, and thelike, may generate or specify a mapping of signature and/or codebooksets to transmitting devices. The generation or specification of themapping may be performed a priori and stored for subsequent use.Alternatively, the mapping may be performed dynamically duringoperations to meet changing operating conditions. The mapping may beprovided to the receiving devices. As an example, UEs may be providedthe mapping when they associate with an eNB of the communicationssystem. As another example, after providing the initial mapping,subsequent mappings may be broadcast or multicast to the receivingdevices as the mapping is adjusted or changed.

Generally, a receiving device, such as a UE receiving a downlinktransmission or an eNB receiving an uplink transmission, may need toknow potentially active signature and/or codebook sets from transmittingdevices that will be transmitting to it, i.e., the transmitting devicesthat are in its cooperating set (e.g., a CoMP set). The receiving devicemay utilize centric transmitting device selection, which is similar toCRAN best transmit point selection. The receiving device may obtaininformation regarding the potentially active signature and/or codebooksets from its cooperation set configuration and the mapping of signatureand/or codebook sets to transmitting devices provided to it when itassociated with an eNB or through broadcasts or multicasts.

FIG. 10 a illustrates a communications system 1000 whereinter-transmitter coordinated beamforming (CBF) is used with open-loopMIMO CSM. Communications system 1000 includes transmitting devices, suchas transmitter 1005 and transmitter 1007, and receiving devices, such asUE 1015, UE 1017, UE 1020, and UE 1022. Uncoordinated transmissions mayresult in high levels of interference between neighboring transmittingdevices. Generally, CBF involves the coordination of transmissionbeamforms used by multiple transmitting devices so that interference toneighboring transmitting devices is reduced or eliminated. Differenttransmitting devices, such as transmitter 1005 and transmitter 1007, mayapply receiving device group based precoders to produce a transmissionbeamform, such as beamform 1010 or beamform 1012, to reduce interferenceto its neighboring transmitting devices. As shown, transmitter 1005 mayselect beamform 1010 to transmit to receiving devices, such as UE 1015and UE 1017, so that it reduces interference to transmissions oftransmitter 1007 to receiving devices, such as UE 1020 and UE 1022,using beamform 1012. It is noted that the precoders (and therefore, theresulting beamforms) may change over time and/or frequency to reduce oreliminate interference to other neighboring transmitting devices.Remaining interference may be cancelled at the receiving devices throughthe use of a SCMA decoder, such as a MPA decoder. The performance may befurther improved through thoughtful signature and/or codebook setassignments.

FIG. 10 b illustrates a communications system 1050 whereintra-transmitter CBF is used with open-loop MIMO CSM. Communicationssystem 1050 includes a transmitting device 1055 serving receivingdevices, such as UE 1060, UE 1062, UE 1065, and UE 1067. As withinter-transmitter CBF, uncoordinated transmissions from the transmitantennas of a single transmitting device may cause interference with oneanother. Intra-transmitter CBF involves coordination of transmissionbeamforms used by the transmit antennas of a transmitting device toreduce or eliminate interference to other transmit antennas of the sametransmitting device. Different transmit antennas, such as antenna 1070and antenna 1072, may apply receiving device group based precoders toproduce a transmission beamform, such as beamform 1075 and beamform1077, to reduce interference to its other transmit antennas. As shown,transmit antenna 1070 may select beamform 1075 to its receiving devices,such as UE 1060 and UE 1062, so that it reduces interference totransmissions of transmit antenna 1072 to receiving devices, such as UE1065 and UE 1067, using beamform 1077. The use of receiving device groupbased precoders enable co-transmission to multi-SCMA receiving devices.Remaining interference may be cancelled at the receiving devices throughthe use of a SCMA decoder, such as a MPA decoder. The performance may befurther improved through thoughtful signature and/or codebook setassignments.

FIG. 11 a illustrates a model 1100 of a transmitting device-receivingdevice pair for implementation of block-wise space-time coding in MIMOSCMA where the receiving device has low complexity. Model 1100 includesa transmitting device 1105 and a receiving device 1110 coupled togetherby a communications channel, H. Transmitting device 1105 and receivingdevice 1110 include circuitry to support transmit diversity for MIMOSCMA OFDM through the use of block-wise space-time coding. In general,space-time coding employs the transmission, by a transmitting device, ofmultiple redundant copies of data over the communications channel H tohelp improve the reliability of data transmission. With the transmissionof multiple copies of the data, it is thought that some of the copieswill successfully arrive at a receiving device, thereby allowing thedata to be recovered.

Transmitting device 1105 includes a SCMA modulator 1120 that encodes adata symbol u, producing a SCMA symbol block 1122. SCMA symbol block1122 is shown as including four tones, two of which are non-zero.However, other configurations are possible. Other configurations includedifferent number of tones, as well as different number (and location) ofnon-zero tones. SCMA symbol block 1122 is provided to a block-wisespace-time encoder 1125 which typically encodes SCMA symbol block 1122 ablock at a time. Block-wise space-time encoder 1125 may also provide acoding gain in addition to the diversity gain. Block-wise space-timeencoder 1125 may be able to utilize available space-time codes, withspreading being performed in multi-carrier time and/or frequencydomains. It is also possible to achieve double domain diversity in bothtime and/or frequency and space domains. Transmitting device 1105transmits the data symbol u as encoded by block-wise space-time encoder1125.

Receiving device 1110 includes a block-wise space-time decoder 1130decodes a received version of the encoded data symbol u. Block-wisespace-time decoder 1130 may be able to decode a the received version ofthe encoded data symbol u, from a version of BWST symbol (or a block ofmultiplexed BWST symbols) transmitted by transmitting device 1105.Block-wise space-time decoder 1130 may be able to exploit the transmitdiversity inherent in the space-time coding to recover from errorsand/or interference present in the communications channel H to produceone or more SCMA symbol blocks from the BWST symbol or block ofmultiplexed BWST symbols. A channel equalizer and SCMA decoder 1135recovers the data symbol u from the one or more SCMA symbol blocks.

FIG. 11 b illustrates a model 1150 of a transmitting device-receivingdevice pair for implementation of block-wise space-time coding in MIMOSCMA where the receiving device has high complexity. Model 1150 includesa transmitting device 1155 and a receiving device 1160 coupled togetherby a communications channel, H. Transmitting device 1155 and receivingdevice 1160 include circuitry to support transmit diversity for MIMOSCMA OFDM through the use of block-wise space-time coding. In general,space-time coding employs the transmission, by a transmitting device, ofmultiple redundant copies of data over the communications channel H tohelp improve the reliability of data transmission. With the transmissionof multiple copies of the data, it is thought that some of the copieswill successfully arrive at a receiving device, thereby allowing thedata to be recovered.

Transmitting device 1155 includes a SCMA modulator 1170 that encodes adata symbol u, producing a SCMA symbol block 1172. SCMA symbol block1172 is shown as including four tones, two of which are non-zero.However, other configurations are possible. Other configurations includedifferent number of tones, as well as different number (and location) ofnon-zero tones. SCMA symbol block 1172 is provided to a block-wisespace-time encoder 1175 which typically encodes SCMA symbol block 1172 ablock at a time. Block-wise space-time encoder 1175 may also provide adiversity gain in addition to the coding gain. Block-wise space-timeencoder 1175 may be able to utilize available space-time codes, withspreading being performed in multi-carrier time and/or frequencydomains. It is also possible to achieve double domain diversity in bothtime and/or frequency and space domains. Transmitting device 1155transmits the data symbol u as encoded by block-wise space-time encoder1175.

Receiving device 1160 includes a joint block-wise space-time and SCMAdecoder 1180 that jointly decodes a received version of the encoded datasymbol u. Joint block-wise space-time and SCMA decoder 1180 may be ableto jointly decode the data symbol u from the received version of theBWST symbol (or a block of multiplexed BWST symbols) and exploit thetransmit diversity inherent in the space-time coding to recover fromerrors and/or interference present in the communications channel H.

FIG. 12 a illustrates a flow diagram of operations 1200 occurring in atransmitting device as the transmitting device transmits data usingblock-wise space-time coding. Operations 1200 may be indicative ofoperations occurring in a transmitting device, such as transmittingdevice 205, as the transmitting device transmits data using block-wisespace-time (BWST) coding.

Operations 1200 may begin with the transmitting device generating a SCMAsymbol block from data symbol(s) (block 1205). As an example, datasymbol u (a part of a bit stream or data stream) may be mapped (orencoded) to produce a SCMA symbol block. The transmitting device maygenerate a BWST symbol from the SCMA symbol block (block 1207). The BWSTsymbol may be encoded from the SCMA symbol block a block at a time.Coding gain may be provided in addition to diversity gain. Thetransmitting device may transmit the BWST symbol (block 1209).

FIG. 12 b illustrates a flow diagram of operations 1230 occurring in areceiving device with low complexity as the receiving device receivesdata using block-wise space-time coding. Operations 1230 may beindicative of operations occurring in a receiving device, such asreceiving device 210, as the receiving device receives data using BWSTcoding.

Operations 1230 may begin with the receiving device determining aplurality of codebooks (block 1235). The plurality of codebooks isassociated with a transmitting device that is transmitting data to thereceiving device. The receiving device may receive a BWST symbol or ablock of multiplexed BWST symbols (block 1237). The receiving device mayuse a BWST decoder to decode the BWST symbol or block of multiplexedBWST symbols to produce one or more SCMA symbol blocks (block 1239). Thereceiving device may use a channel equalizer and SCMA decoder to recovera version of the data symbols from the one or more SCMA symbol block(block 1241). Blocks 1239 and 1241 may be collectively referred to asprocessing the BWST symbol using

FIG. 12 c illustrates a flow diagram of operations 1260 occurring in areceiving device with high complexity as the receiving device receivesdata using block-wise space-time coding. Operations 1260 may beindicative of operations occurring in a receiving device, such asreceiving device 210, as the receiving device receives data using BWSTcoding.

Operations 1260 may begin with the receiving device determining aplurality of codebooks (block 1265). The plurality of codebooks isassociated with a transmitting device that is transmitting data to thereceiving device. The receiving device may receive a BWST symbol or ablock of multiplexed BWST symbols (block 1267). The receiving device mayuse a joint BWST and SCMA decoder to jointly decode the BWST symbol orblock of multiplexed BWST symbols to produce a version of the datasymbols (block 1269).

FIG. 13 a illustrates a symbol 1300 of an example MIMO SCMA OFDMcommunications system. Symbol 1300 may be an example transmission blockof a MIMO SCMA OFDM communications system with a transmission devicewith 2 transmit antenna and a receiving device with 1 receive antennawhere the Alamouti algorithm is used. With such a configuration, acommunications channel H between the transmitting device and thereceiving device may be expressible as:

H=[h ₁ h ₂],

where h₁ is the communications channel for a first transmit antenna andh₂ is the communications channel for the second transmit antenna.

Symbol 1300 comprises two SCMA blocks, SCMA BLK₁ and SCMA BLK₂. EachSCMA block includes two SCMA codewords, one for each transmit antenna.As shown in FIG. 13 a, a SCMA codeword comprises four resource elements(RE) with two REs being non-zero and two REs being zero. It is notedthat other SCMA codeword configurations are possible, e.g., differentnumber of REs, different number of non-zero REs, different number ofzero REs, and the like.

FIG. 13 b illustrates a model 1350 of a transmitting device-receivingdevice pair using an Alamouti algorithm for block-wise space-timecoding. Model 1350 includes a transmitting device 1355 and a receivingdevice 1360 coupled together by a communications channel, H.Transmitting device 1355 and receiving device 1360 include circuitry tosupport transmit diversity for MIMO SCMA OFDM through the use ofblock-wise space-time coding using the Alamouti algorithm.

Transmitting device 1355 includes a SCMA modulator 1365 that encodes adata symbol u, producing a SCMA codeword. The SCMA codeword is shown asincluding four REs, two of which are non-zero. However, otherconfigurations are possible. Other configurations include differentnumber of REs, as well as different number (and location) of non-zeroREs. The SCMA codeword is provided to a block-wise Alamouti encoder 1370which typically encodes the SCMA codeword a block at a time. Block-wiseAlamouti encoder 1370 may also provide a coding gain in addition to thediversity gain. Block-wise Transmitting device 1355 transmits the datasymbol u as encoded by block-wise Alamouti encoder 1370. Receivingdevice 1360 includes a block-wise Alamouti decoder 1375 decodes areceived version of the encoded data symbol u. Block-wise Alamoutidecoder 1375 may be able to decode from the received version of theencoded data symbol u a version of the SCMA codeword. Block-wiseAlamouti decoder 1375 may be able to exploit the transmit diversityinherent in the space-time coding to recover from errors and/orinterference present in the communications channel H. A channelequalizer and SCMA decoder 1380 recovers the data symbol u from theversion of the SCMA codeword. It is noted that with the use of theAlamouti algorithm, the equivalent channel for each symbol isexpressible as:

√{square root over (|h ₁|² +|h ₂|²)}.

According to another example embodiment, the channel equalization,block-wise Alamouti decoding and SCMA decoding may be performed jointly.

FIG. 14 illustrates a first communications device 1400. Communicationsdevice 1400 may be an implementation of transmitting device, such as aneNB, an access point, a communications controller, a base station, andthe like, or a UE, a mobile, a mobile station, a terminal, a user, asubscriber, and the like. Communications device 1400 may be used toimplement various ones of the embodiments discussed herein. As shown inFIG. 14, a transmitter 1405 is configured to transmit packets, and thelike, using open-loop CSM for MIMO SCMA OFDM. Communications device 1400also includes a receiver 1410 that is configured to receive packets, andthe like.

An encoder 1420 is configured to encode data layers for multipletransmit antennas using signature and/or codebook sets with each datalayer being encoded with a sub-signature and/or subcodebook set. Acombiner 1422 is configured to combine encoded data from encoder 1420into output codewords. Combiner 1422 is configured to multiplex encodeddata from multiple data layers into the output codewords or map encodeddata from a single data layer into the output codewords. A codebookprocessing unit 1424 is configured to retrieve signature and/or codebooksets. Codebook processing unit 1424 is configured to select signatureand/or codebook sets in accordance with mappings of transmitting devicesand/or transmit antennas to signature and/or codebook sets. A memory1430 is configured to store data, signature and/or codebook sets,mappings of signature and/or codebook sets to transmitting devicesand/or transmit antennas, and the like.

The elements of communications device 1400 may be implemented asspecific hardware logic blocks. In an alternative, the elements ofcommunications device 1400 may be implemented as software executing in aprocessor, controller, application specific integrated circuit, or soon. In yet another alternative, the elements of communications device1400 may be implemented as a combination of software and/or hardware.

As an example, receiver 1410 and transmitter 1405 may be implemented asa specific hardware block, while encoder 1420, combiner 1422, andcodebook processing unit 1424 may be software modules executing in amicroprocessor (such as processor 1415) or a custom circuit or a customcompiled logic array of a field programmable logic array. Encoder 1420,combiner 1422, and codebook processing unit 1424 may be modules storedin memory 1430.

FIG. 15 illustrates a second communications device 1500. Communicationsdevice 1500 may be an implementation of receiving device, such as a UE,a mobile, a mobile station, a terminal, a user, a subscriber, and thelike, or an eNB, an access point, a communications controller, a basestation, and the like. Communications device 1500 may be used toimplement various ones of the embodiments discussed herein. As shown inFIG. 15, a transmitter 1505 is configured to transmit packets, and thelike. Communications device 1500 also includes a receiver 1510 that isconfigured to receive packets, and the like, using open-loop CSM forMIMO SCMA OFDM.

A MIMO processing unit 1520 is configured to separate different datalayers present in a received signal. MIMO processing unit 1520 may use aMMSE algorithm, a MRC algorithm, and the like, to separate the differentdata layers. A SCMA detecting unit 1522 is configured to detectcodewords present in the received signal (or different data layers ofthe received signal) to recover data transmitted to communicationsdevice 1500. SCMA detecting unit 1522 may use a low complexityalgorithm, such as MPA, turbo decoding, and the like, to recover thedata. It is noted that MIMO processing unit 1520 and SCMA detecting unit1522 may be implemented as separate units or a single combination unit.A codebook processing unit 1524 is configured to determine potentiallyactive signature and/or codebook sets. A memory 1530 is configured tostore data, signature and/or codebook sets, mappings of signature and/orcodebook sets to transmitting devices and/or transmit antennas, and thelike.

The elements of communications device 1500 may be implemented asspecific hardware logic blocks. In an alternative, the elements ofcommunications device 1500 may be implemented as software executing in aprocessor, controller, application specific integrated circuit, or soon. In yet another alternative, the elements of communications device1400 may be implemented as a combination of software and/or hardware.

As an example, receiver 1510 and transmitter 1505 may be implemented asa specific hardware block, while MIMO processing unit 1520, SCMAdetecting unit 1522, and codebook processing unit 1524 may be softwaremodules executing in a microprocessor (such as processor 1515) or acustom circuit or a custom compiled logic array of a field programmablelogic array. MIMO processing unit 1520, SCMA detecting unit 1522, andcodebook processing unit 1524 may be modules stored in memory 1530.

FIG. 16 illustrates a third communications device 1600. Communicationsdevice 1400 may be an implementation of transmitting device, such as aneNB, an access point, a communications controller, a base station, andthe like, or a UE, a mobile, a mobile station, a terminal, a user, asubscriber, and the like. Communications device 1600 may be used toimplement various ones of the embodiments discussed herein. As shown inFIG. 16, a transmitter 1605 is configured to transmit packets, and thelike, using BWST SCMA OFDM. Communications device 1600 also includes areceiver 1610 that is configured to receive packets, and the like.

A modulator 1620 is configured to encode data layers for multipletransmit antennas using signature and/or codebook sets with each datalayer being encoded with a sub-signature and/or subcodebook set. A BWSTencoder 1622 is configured to combine SCMA symbol blocks (encoded data)from modulator 1620 into output codewords. BWST encoder 1622 isconfigured to combine the SCMA symbol blocks from multiple data layersinto the output codewords or the SCMA symbol block from a single datalayer into the output codewords. A codebook processing unit 1624 isconfigured to retrieve signature and/or codebook sets. Codebookprocessing unit 1624 is configured to select signature and/or codebooksets in accordance with mappings of transmitting devices and/or transmitantennas to signature and/or codebook sets. A memory 1630 is configuredto store data, signature and/or codebook sets, mappings of signatureand/or codebook sets to transmitting devices and/or transmit antennas,and the like.

The elements of communications device 1600 may be implemented asspecific hardware logic blocks. In an alternative, the elements ofcommunications device 1600 may be implemented as software executing in aprocessor, controller, application specific integrated circuit, or soon. In yet another alternative, the elements of communications device1600 may be implemented as a combination of software and/or hardware.

As an example, receiver 1610 and transmitter 1605 may be implemented asa specific hardware block, while modulator 1620, BWST encoder 1622, andcodebook processing unit 1624 may be software modules executing in amicroprocessor (such as processor 1615) or a custom circuit or a customcompiled logic array of a field programmable logic array. Modulator1620, BWST encoder 1622, and codebook processing unit 1624 may bemodules stored in memory 1630.

FIG. 17 illustrates a fourth communications device 1700. Communicationsdevice 1700 may be an implementation of receiving device, such as a UE,a mobile, a mobile station, a terminal, a user, a subscriber, and thelike, or an eNB, an access point, a communications controller, a basestation, and the like. Communications device 1700 may be used toimplement various ones of the embodiments discussed herein. As shown inFIG. 17, a transmitter 1705 is configured to transmit packets, and thelike. Communications device 1700 also includes a receiver 1710 that isconfigured to receive packets, and the like, using BWST SCMA OFDM.

A BWST decoder 1720 is configured to separate different data layerspresent in a received signal. BWST decoder 1720 may use the Alamoutialgorithm, and the like, to separate the different data layers. A SCMAdetecting unit 1722 is configured to detect codewords present in thereceived signal (or different data layers of the received signal) torecover data transmitted to communications device 1700. SCMA detectingunit 1722 may use a low complexity algorithm, such as MPA, turbodecoding, and the like, to recover the data. It is noted BWST decoder1720 and SCMA detecting unit 1722 may be implemented as separate unitsor a single combination unit. A codebook processing unit 1724 isconfigured to determine potentially active signature and/or codebooksets. A memory 1730 is configured to store data, signature and/orcodebook sets, mappings of signature and/or codebook sets totransmitting devices and/or transmit antennas, and the like.

The elements of communications device 1700 may be implemented asspecific hardware logic blocks. In an alternative, the elements ofcommunications device 1700 may be implemented as software executing in aprocessor, controller, application specific integrated circuit, or soon. In yet another alternative, the elements of communications device1700 may be implemented as a combination of software and/or hardware.

As an example, receiver 1710 and transmitter 1705 may be implemented asa specific hardware block, while BWST decoder 1720, SCMA detecting unit1722, and codebook processing unit 1724 may be software modulesexecuting in a microprocessor (such as processor 1715) or a customcircuit or a custom compiled logic array of a field programmable logicarray. BWST decoder 1720, SCMA detecting unit 1722, and codebookprocessing unit 1724 may be modules stored in memory 1730.

Advantageous features of the embodiments may include: a transmittingdevice including a processor and a transmitter operatively coupled tothe processor. The processor configured to map a coded information bitstream intended for a transmit antenna onto at least one spreadingsequence of a plurality of spreading sequences to produce a data stream,and to encode the data stream using a space-time code to produce asymbol block; and the transmitter configured to transmit the symbolblock. The processor is also configured to encode the coded informationbit stream by selecting the at least one spreading sequence from theplurality of spreading sequences to produce the data stream. Theprocessor is also configured to encode one portion of the codedinformation bit stream for a first data layer by selecting a firstspreading sequence from a first subset of the plurality of spreadingsequences corresponding to the first data layer, to encode anotherportion of the coded information bit stream for a second data layer byselecting a second spreading sequence from a second subset of theplurality of spreading sequences corresponding to the second data layer,and to combine the first spreading sequence and the second spreadingsequence to produce the data stream.

Advantageous features of the embodiments may include: a receiving deviceincluding a processor and a receiver operatively coupled to theprocessor. The processor configured to determining a plurality ofcodebooks, wherein the plurality of codebooks is associated with atransmitting device transmitting data to the receiving device, to decodea symbol block using a space-time code to produce a codespace symbol,and to process the codespace symbol using the plurality of codebooks torecover the data. The receiver configured to receive a symbol block fromthe transmitting device. The processor is also configured to decode thesymbol block using an Alamouti algorithm. The processor is alsoconfigured to despread the symbol block in at least one of a frequencydomain and a time domain.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims.

What is claimed is:
 1. A method for transmitting data comprising:selecting, by a transmitting device, a plurality of spreading sequencesin accordance with a communications channel; mapping, by a transmittingdevice, a plurality of portions of a coded information bit stream ontorespective ones of the plurality of spreading sequences to generate aplurality of data streams; multiplexing, by the transmitting device, theplurality of data streams into a combined communications stream; andtransmitting, by the transmitting device, the combined communicationsstream over the communications channel.
 2. The method of claim 1,wherein the plurality of spreading sequences comprise low densitysequence (LDS) signatures.
 3. The method of claim 1, wherein theplurality of spreading sequences comprise codewords of sparse codemultiple access (SCMA) codebooks.
 4. The method of claim 1, whereinmapping the plurality of portions of the coded information bit streamcomprises: dividing each portion of the coded information bit streaminto groups of binary values; and selecting codes from the respectiveone of the plurality of spreading sequences that correspond to eachgroup of binary values.
 5. The method of claim 1, wherein each portionof the plurality of portions of the coded information bit stream aredisjoint.
 6. The method of claim 1, further comprising: selecting, bythe transmitting device, a precoder, the precoder being selected toreduce interference to receiving devices that are not intendedrecipients of the data streams; and precoding, by the transmittingdevice, each portion of the coded information bit stream in accordancewith the precoder.
 7. The method of claim 6, wherein the precoder is ablockwise space-time encoder.
 8. The method of claim 6, wherein theprecoder is a block-wise Alamouti encoder.
 9. A method for transmittingdata comprising: selecting, by a transmitting device, a first pluralityof data layers to transmit on a first communications channel, and asecond plurality of data layers to transmit on a second communicationschannel; mapping, by the transmitting device, the first plurality ofdata layers onto a first plurality of spreading sequences to produce afirst data stream, each data layer being mapped according to at leastone spreading sequence in the first plurality of spreading sequences;mapping, by the transmitting device, the second plurality of data layersonto a second plurality of spreading sequences to produce a second datastream, each data layer being mapped according to at least one spreadingsequence in the second plurality of spreading sequences; andtransmitting, by the transmitting device, the first data stream on thefirst communications channel, and the second data stream on the secondcommunications channel.
 10. The method of claim 9, wherein the firstplurality of data layers and the second plurality of data layers areselected according to a Quality of Service (QoS) requirement.
 11. Themethod of claim 9, wherein the first plurality of spreading sequencesare chosen in accordance with the first communications channel, and thesecond plurality of spreading sequences are chosen in accordance withthe second communications channel.
 12. The method of claim 9, whereinmapping the first plurality of data layers onto the first plurality ofspreading sequences to produce the first data stream comprisesmultiplexing the mapped first plurality of data layers to produce thefirst data stream.
 13. The method of claim 9, wherein the first datastream and the second data stream are transmitted to a single receivingdevice.
 14. The method of claim 9, wherein the first data stream and thesecond data stream are transmitted to different receiving devices. 15.The method of claim 9, wherein the first communications channel and thesecond communications channel are antennas of the transmitting device.16. The method of claim 9, further comprising: selecting, by thetransmitting device, a precoder to reduce interference to receivingdevices that are not intended recipients of the first data stream andthe second data stream; and precoding, by the transmitting device, thefirst data stream and the second data stream with the precoder.
 17. Themethod of claim 16, wherein precoding with the precoder comprisesencoding using a space-time encoder to produces a symbol block.
 18. Themethod of claim 17, wherein the encoding is performed using an Alamoutialgorithm.
 19. A communications device comprising: an antenna; aprocessor configured to select a plurality of spreading sequences inaccordance with a property of the antenna, and to map a plurality ofportions of a coded information bit stream onto respective ones of theplurality of spreading sequences to generate a plurality of datastreams; a multiplexer coupled to the processor, the multiplexerconfigured to mux the plurality of data streams into a combinedcommunications stream; and a transmitter coupled to the multiplexer andthe antenna, the transmitter configured to transmit the combinedcommunications stream over the antenna.
 20. The communications device ofclaim 19, wherein the processor is further configured to select a lowdensity sequence (LDS) signature when selecting a plurality of spreadingsequences.
 21. The communications device of claim 20, wherein theprocessor is further configured to select a sparse code multiple access(SCMA) codebook when selecting a plurality of spreading sequences. 22.The communications device of claim 20, further comprising: a precodercoupled to the processor and the transmitter, the precoder configured toencode each portion of the coded information bit stream to reduceinterference to receiving devices that are not intended recipients ofthe data streams.
 23. A communications device comprising: a firstantenna; a second antenna; a processor configured to select, a firstplurality of data layers to transmit on the first antenna, and a secondplurality of data layers to transmit on the second antenna, theprocessor further configured to map the first plurality of data layersonto a first plurality of spreading sequences to produce a first datastream, each data layer being mapped according to at least one spreadingsequence in the first plurality of spreading sequences, the processorfurther configured to map the second plurality of data layers onto asecond plurality of spreading sequences to produce a second data stream,each data layer being mapped according to at least one spreadingsequence in the second plurality of spreading sequences; and atransmitter coupled to the processor, the first antenna, and the secondantenna, the transmitter configured to transmit the first data stream onthe first antenna, and the second data stream on the second antenna. 24.The communications device of claim 23, wherein the processor is furtherconfigured to select the first plurality of spreading sequences inaccordance with a property of the first antenna, and the secondplurality of spreading sequences in accordance with a property of thesecond antenna.
 25. The communications device of claim 23, furthercomprising: a multiplexer coupled to the processor and transmitter, themultiplexer configured to produce the first data stream by mixing thefirst plurality of data layers after mapping of the first plurality ofdata layers.